Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX

[Baoquan he]

On 12/10/24 at 02:43pm, Sourabh Jain wrote:
> kexec_elf_load() loads an ELF executable and sets the address of the
> lowest PT_LOAD section to the address held by the lowest_load_addr
> function argument.
> 
> To determine the lowest PT_LOAD address, a local variable lowest_addr
> (type unsigned long) is initialized to UINT_MAX. After loading each
> PT_LOAD, its address is compared to lowest_addr. If a loaded PT_LOAD
> address is lower, lowest_addr is updated. However, setting lowest_addr
> to UINT_MAX won't work when the kernel image is loaded above 4G, as the
> returned lowest PT_LOAD address would be invalid. This is resolved by
> initializing lowest_addr to ULONG_MAX instead.
> 
> This issue was discovered while implementing crashkernel high/low
> reservation on the PowerPC architecture.
> 
> Fixes: a0458284f062 ("powerpc: Add support code for kexec_file_load()")
> Cc: Baoquan he <bhe@xxxxxxxxxx>
> Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> CC: Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
> ---
>  kernel/kexec_elf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kexec_elf.c b/kernel/kexec_elf.c
> index d3689632e8b9..3a5c25b2adc9 100644
> --- a/kernel/kexec_elf.c
> +++ b/kernel/kexec_elf.c
> @@ -390,7 +390,7 @@ int kexec_elf_load(struct kimage *image, struct elfhdr *ehdr,
>  			 struct kexec_buf *kbuf,
>  			 unsigned long *lowest_load_addr)
>  {
> -	unsigned long lowest_addr = UINT_MAX;
> +	unsigned long lowest_addr = ULONG_MAX;

Great catch.

Acked-by: Baoquan He <bhe@xxxxxxxxxx>

>  	int ret;
>  	size_t i;
>  
> -- 
> 2.47.1
>